The work deals with renewal processes in the visual cells and pigment epithelium in the vertebrate retina. Particular attention is currently devoted to the analysis of daily rhythms in ultrastructure and metabolism of rods and cones in goldfish and frog, using electron microscopic analysis of retinas from animals maintained on a daily light cycle, and using autoradiographic analysis of animals kept on a comparable light cycle and injected at different times of day with precursors of important biological molecules (such as RNA and protein). Some in vitro studies are also under way.